FATIGUE AND CORROSION FATIGUE OF 8090 Al-Li-Cu-Mg ALLOY

The fatigue resistance of metals can be profoundly affected by the environmental reactions that change crack initiation and propagation processes. These corrosion fatigue processes can occur in high strength aluminium alloys in aircraft, which frequently encounter salt spray and high humidity environments. For this reason, the fatigue behaviour of 8090-T6 alloy in the form of 25mm thick plate has been investigated in both air and an aerated 2.5% NaCl solution. Results are compared to a conventional high strength aluminium alloy, 2014-T6. Fatigue crack initiation and propagation data are presented for different crack orientations and mean stress levels. The slightly lower fatigue strength of 8090-T6 in air is attributed to earlier crack initiation. The fatigue crack propagation behaviour of 8090-T6 is shown to be superior to that of 2014-T6 at low to intermediate levels of ƊK, under both environmental conditions. The mechanisms associated with fatigue crack initiation and propagation, and environmental effects, are discussed.